1. Field of the Invention
The present invention relates to techniques for a semiconductor integrated circuit and its driving method. The invention also relates to a light-emitting device that has a semiconductor integrated circuit of the present invention in its driver circuit portion and a pixel portion. In particular, the present invention relates to an active matrix type light-emitting device in which the semiconductor integrated circuit of the present invention is applied to a signal line driver circuit of the driver circuit portion.
2. Description of the Related Art
In recent years, research and development of light-emitting devices using self-light-emitting elements such as organic light-emitting diodes (OLEDs) have progressed. An OLED has an anode and a cathode, and has a structure in which an organic compound layer is sandwiched between the aforementioned anode and cathode. Light-emitting devices using OLEDs have characteristics in that they have suitably fast response speed for animated displays, low voltage, low power consumption driving, or the like. Thus, light-emitting devices using light-emitting elements are expected to be widely used for various purposes, including new-generation mobile telephones and personal digital assistants (PDAs) and are attracting attention as the next-generation displays.
When displaying a multi-gray scale image using a light-emitting device with a self-light-emitting element, a current input method can be given as a driving method thereof. In the current input method, the luminance of the relevant light-emitting element is controlled by writing the current value form data onto the pixel as the image signal. It is possible that the image signal of the current input method is either an analog value (analog driving method) or a digital value (digital driving method).
As a signal line driver circuit with the above-mentioned current input system, for example, a circuit shown in FIG. 10A is proposed (refer to A. Yumoto et al., Proc. Asia Display/IDW '01 pp.1395-1398 (2001)). In FIG. 10A, a pair of current source circuits is provided to each of signal lines. In the structure of the circuit in FIG. 10A, pairs of current source circuits A1 and B1, A2 and B2, . . . are respectively connected with the signal lines. The pair of current source circuits A and B alternately conduct an operation of reading and storing an image signal in a form of a current value (image signal current) and an operation of writing a signal to a pixel through a signal line. That is, while the current source circuit A conducts the operation of reading and setting a signal current, the current source circuit B conducts the operation of writing a signal to a light-emitting element provided in a pixel region through a signal line. Conversely, while the current source circuit A conducts the operation of writing a signal to a light-emitting element provided in a pixel region through a signal line, the current source circuit B conducts the operation of reading and setting a signal current.
Operation timings of the current source circuits A and B are shown in FIG. 10B. FIG. 10B is a schematic block diagram of the following operation. In a k-th row selection period (horizontal period), while the circuit A1 conducts the operation of reading and storing a signal (R1), the circuit B1 conducts the operation of writing a signal to a signal line (W1). Further, in the next (k+1)-th row selection period, while the circuit A1 conducts the operation of writing a signal to a signal line (W1), the circuit B1 conducts the operation of reading and storing a signal (R1). Moreover, FIG. 10C is a schematic diagram of the entire light-emitting device provided with the current source circuit.
However, in the above-mentioned driver circuit, a pair of current source circuits is provided to each signal line. Thus, the area of the current source circuit shown in FIG. 10C is large, and miniaturization of the signal line driver circuit is difficult to be realized. As a result, in the light-emitting device, the proportion of the signal line driver circuit is large, which obstructs reduction in size of a frame and leads to reduction in area of the pixel region.